It is known that an isotropic vibrating rate gyro is constituted by an axially-symmetrical resonator having two degrees of freedom.
The vibrator member of the resonator is set into vibration at the resonant frequency of the vibrator member by an amplitude control signal. To control the orientation of the vibration, a precession control signal is also applied to the vibrator member so that a measurement of the vibration of the vibrator member and demodulation of said vibration at the resonant frequency of the vibrator member make it possible, in application of appropriate equations, to determine the speed of rotation to which the resonator is subjected.
The amplitude control signal and the precession control signal are applied via control electrodes that present drive gain, i.e. the ratio of the amplitude of the force generated by the control signal to the amplitude of that control signal. Similarly, the outlet signal is measured by detector electrodes presenting detector gain, which is the ratio of the vibration amplitude to the corresponding amplitude of the output signal.
The accuracy with which the speed of rotation is calculated is a function of the accuracy of the scale factor of the resonator, where the scale factor is the ratio of the speed of rotation of the resonator to the precession control or to an equivalent output signal.
It is observed that the scale factor varies as a function of the temperature to which the resonator is subjected, and also varies over time as a function of component aging. These variations affect measurement accuracy.
In order to improve the precision of the scale factor, it is known to store tables in the processor unit of the gyro, which tables specify variations in the scale factor as a function of temperature and as a function of resonator age. When the gyro is in use, a temperature measurement thus makes it possible to calibrate the scale factor. Nevertheless, the tables are established on the basis of a predictive model that is not satisfactory, and as a result differences can exist between the variations in the scale factor as stored and the real variations in the scale factor while a gyro is in use.